The moon is reaching what’s known as its “perigee”, the closest approach to earth in its orbit - a mere 221,802 miles away. It will appear 16 percent brighter than the average full moon.
Compared to when it’s on the “apogee” side of its orbit, farthest away from earth, it will be 14 percent bigger and 30 percent brighter.
NASA overview of the May 5 Supermoon
This Supermoon stands out from others due to how close together the perigee and full moon will occur in time. The full moon occurs at 11:34 p.m. eastern and perigee follows at 11:35 p.m.
“The timing is almost perfect,” says NASA.
Writes AccuWeather’s astronomy blogger Daniel Vogler: “I looked back at other Super Moon data and cannot find any closer than that timing-wise, remarkable!”
During the March 19 Supermoon of 2011, the perigee and full moon were 50 minutes apart.
The Supermoon promises higher than normal tides. NASA describes the effect:
A perigee full Moon brings with it extra-high “perigean tides,” but this is nothing to worry about, according to NOAA. In most places, lunar gravity at perigee pulls tide waters only a few centimeters (an inch or so) higher than usual. Local geography can amplify the effect to about 15 centimeters (six inches)
On the other hand, these elevated tides could worsen the effects of a coastal storm. AccuWeather’s Vogle writes:
On average, the tide increases 25% during these times. That’s a lot of water displacement over the course of the day! Not only will we have to watch for coastal flooding if there happens to be a storm brewing nearby, as what happened back in 1962...
Although some astrologers have linked extreme natural disasters to the Supermoon, I reviewed some of the evidence for such a connection last year and was not convinced...
The moon is most impressively viewed when low on the horizon owing to the optical illustion it is bigger than it actually is.